Methods of obtaining ophthalmic lenses providing the eye with reduced aberrations

ABSTRACT

An intraocular lens comprises optical part configured to be implanted in an eye of a subject. The intraocular lens further comprises at least one aspheric surface configured, in combination with a lens in the capsular bag of an eye, to reduce an aberration of a wavefront passing the eye. The aberrations may include astigmatism, coma, and/or spherical aberrations. An aberration of the intraocular lens may be expressed as a linear combination of Zernike polynomial terms that may include a Zernike coefficient a 11 . The Zernike coefficient a 11  may be selected to reduce a spherical aberration of a wavefront passing the eye and/or to compensate for an average value resulting from a predetermined number of estimations of the Zernike coefficient a 11  in a population of corneas and capsular bag lenses.

RELATED APPLICATIONS

This application is a continuation of prior application U.S. applicationSer. No. 10/768,755, filed Jan. 30, 2004, which is a divisional of U.S.application Ser. No. 10/027,703, filed Dec. 21, 2001, now U.S. Pat. No.6,705,729, issued on Mar. 16, 2004, which claims priority to U.S.Provisional Application No. 60/259,981, filed Jan. 5, 2001, and SwedishApplication No. 0004829-8, file Dec. 22, 2000.

FIELD OF INVENTION

The present invention relates to methods of designing and selectingophthalmic lenses that provide the eye with reduced aberrations as wellas lenses capable of providing such visual improvements.

BACKGROUND OF THE INVENTION

Beside first order defocus and astigmatism of the eye a number of othervision defects could be present. For example aberrations of differentorders occur when a wavefront passes a refracting surface. The wavefrontitself becomes aspheric when it passes an optical surface that hasimperfections and vision defects occur when an aspheric wavefront fallson the retina. Both the cornea and the lens in the capsular bagcontribute thus to these types of vision defects if they deviate frombeing perfect or perfectly compensating optical elements. The termaspheric will in this text include both asphericity and asymmetry. Anaspheric surface could be either a rotationally symmetric or arotationally asymmetric surface and/or an irregular surface, i.e. allsurfaces not being spherical.

It is presently discussed that the visual quality of eyes having animplanted intraocular lens (IOL) is comparable with normal eyes in apopulation of the same age. Consequently, a 70-year-old cataract patientcan only expect to obtain the visual quality of a non-cataracteousperson of the same age after surgical implantation of an intraocularlens, although such lenses objectively have been regarded as opticallysuperior to the natural crystalline lens. This result can be explainedby the fact that present IOLs are not adapted to compensate forage-related defects of the optical system of the human eye. Age-relateddefects of the eye have also recently been investigated and it is foundthat contrast sensitivity significantly declines in subjects older than50 years. These results seem to comply with the above-mentioneddiscussion, since the contrast sensitivity measurements indicate thatindividuals having undergone cataract surgery with lens implantationwill not obtain a better contrast sensitivity than persons of an averageage of about 60 to 70 years.

Even if intraocular lenses aimed to substitute the defective cataractlens and other ophthalmic lenses, such as conventional contact lenses orintraocular correction lenses, have been developed with excellentoptical quality, it is obvious that they fail to correct for a number ofaberration phenomena of the eye including age-related aberrationdefects.

U.S. Pat. No. 5,777,719 (Williams et al.) discloses a method and anapparatus for accurately measuring higher aberrations of the eye as anoptical system with wavefront analysis. By using a Hartmann-Shackwavefront sensor, it is possible to measure higher order aberrations ofthe eye and using such data to find compensation for these aberrationsand thereby obtain sufficient information for the design of an opticallens which can provide a highly improved optical correction. TheHartmann-Shack sensor provides means for obtaining light reflected fromthe retina of the eye of a subject. The wavefront in the plane of thepupil is recreated in the plane of the lenslet array of theHartmann-Shack sensor. Each lenslet in the array is used to form anaerial image of the retinal point source on a CCD camera located at thefocal plane of the array. The wave aberration of the eye, in the form ofa point source produced on the retina by a laser beam, displaces eachspot by an amount proportional to the local slope of the wavefront ateach of the lenslets. The output from the CCD camera is sent to acomputer, which then performs calculations to fit slope data to thefirst derivatives of 65 Zernike polynomials. From these calculations,coefficients for weighting the Zernike polynomials are obtained. The sumof the weighted Zernike polynomials represents a reconstructed wavefrontdistorted by the aberrations of the eye as an optical system. Theindividual Zernike polynomial terms will then represent different modesof aberration.

U.S. Pat. No. 5,050,981 (Roffman) discloses another method for designinga lens by calculating modulation transfer functions from tracing a largenumber of rays through the lens-eye system and evaluating thedistribution density of the rays in the image position. This isrepeatedly performed by varying at least one lens surface until a lensis found which results in a sharp focus and a minimum of imageaberrations.

The methods referred to above for designing are suitable for the designof contact lenses or other correction lenses for the phakic eye whichcan be perfected to compensate for the aberration of the whole eyesystem. However, to provide improved intraocular lenses adapted to beplaced between the cornea and the capsular bag, in the anterior chamberor in the posterior chamber, it would be necessary to consider theaberrations of the individual parts of the eye.

There has recently been a focus on studying the aberrations of the eye,including a number of studies of the development of these aberrations asa function of age. In one particular study, the development of thecomponents of the eye were examined separately, leading to theconclusion that the optical aberrations of the individual components ofyounger eyes cancel each other out, see Optical Letters, 1998, Vol.23(21), pp. 1713-1715. Also the article of S. Patel et al in Refractive& Corneal Surgery, 1993, Vol. 9, pages 173-181 discloses the asphericityof posterior corneal surfaces. It is suggested that the corneal data canbe used together with other ocular parameters to predict the power andthe asphericity of an intraocular lens with the purpose of maximizingthe optical performances of the future pseudophakic eye. Furthermore, itwas also recently observed by Antonio Guirao and Pablo Artal in IOVS,1999, Vol. 40(4), S535 that the shape of the cornea changes with age andbecomes more spherical. These studies indicate that cornea in thesubjects provides a positive spherical aberration which increases withthe age. In Vision Research, 1998, 38(2), pp. 209-229, A Glasser et al.investigated the spherical aberration of natural crystalline lenses fromeyes obtained from an eye bank after that the corneas had been removed.According to the laser scanner optical method used herein it was foundthat the spherical aberration from an older lens (66 years) showsuncorrected (positive) spherical aberration, whereas a 10-year-old lensshows over-corrected (negative) spherical aberration.

In view of the foregoing, it is apparent that there is a need forophthalmic lenses that are better adapted to compensate the aberrationscaused by the individual surfaces of eye, such as the corneal surfacesand the surfaces of the lens in the capsular bag, and capable of bettercorrecting aberrations other than defocus and astigmatism, as isprovided with conventional ophthalmic lenses.

DESCRIPTION OF THE INVENTION

It is an object of the invention to improve the visual quality of eyes.

It is a further object of the invention to provide for methods thatresult in obtaining an ophthalmic lens, which provides the eye withreduced aberrations.

It is another object of the invention to provide methods of obtaining anintraocular lens capable of reducing the aberration of the eye after itsimplantation into the eye.

It is a further object to provide for methods of obtaining anintraocular lens capable of compensating for the aberrations resultingfrom optical irregularities in the corneal surfaces and the surfaces ofthe lens in the capsular bag.

It is a still further object of the present invention to provide anintraocular lens which, together with a lens in the capsular bag, iscapable of restoring a wavefront deviating from sphericity into asubstantially more spherical wavefront.

It is a further object of the invention to provide an intraocular lens,which improves the visual quality for patients who have undergone acorneal surgery or who have corneal defects or diseases.

The present invention generally relates to methods of obtaining anophthalmic lens that is capable of reducing the aberrations of the eye.By aberrations in this context is meant wavefront aberrations. This isbased on the understanding that a converging wavefront must be perfectlyspherical to form a point image, i.e. if a perfect image shall be formedon the retina of the eye, the wavefront having passed the opticalsurfaces of the eye, such as the cornea and the natural lens must beperfectly spherical. An aberrated image will be formed if the wavefrontdeviates from being spherical and this is the case when it has passed anon perfect lens system. The wavefront aberration can be expressed inmathematical terms in accordance with different approximate models as isexplained in textbook references, such as M. R. Freeman Optics, TenthEdition, 1990.

In a first embodiment, the present invention is directed to a method ofdesigning an intraocular lens capable of reducing aberrations of an eyeafter its implantation. The method comprises a first step of measuringthe wavefront aberration of the uncorrected eye using a wavefrontsensor. The shape of at least one corneal surface in the eye is alsomeasured using a corneal topographer. The at least one corneal surfaceand a lens located in the capsular bag of the eye comprising said corneaare then characterized as a mathematical model and by employing thismathematical model the resulting aberrations of the corneal surface andthe lens in the capsular bag are calculated. The lens in the capsularbag can be either the natural lens or an implanted lens of any kind.Hereafter the lens in the capsular bag will be called the capsular baglens. An expression of the aberrations of the cornea and the capsularbag lens is thereby obtained, i.e. the wavefront aberrations of awavefront having passed such a corneal surface and such a lens.Dependent on the selected mathematical model, different routes tocalculate the aberrations can be taken. Preferably, the corneal surfaceand the capsular bag lens are characterized as mathematical models interms of a conicoid of rotation or in terms of polynomials or acombination thereof. More preferably, the corneal surface and thecapsular bag lens are characterized in terms of linear combinations ofpolynomials. The second step of the method is to select the power of theintraocular correction lens, which is done according to conventionalmethods for the specific need of optical correction of the eye. From theinformation of steps one and two an intraocular correction lens ismodeled, such that a wavefront from an optical system comprising saidcorrection lens and the mathematical models of the cornea and thecapsular bag lens obtains reduced aberrations. The optical systemconsidered when modeling the lens typically includes the cornea, thecapsular bag lens and said correction lens, but in the specific case itcan also include other optical elements including the lenses ofspectacles, or an artificial correction lens, such as a contact lens oran implantable correction lens depending on the individual situation.

Modeling the lens involves selection of one or several lens parametersin a system which contributes to the determination of the lens shape ofa given, pre-selected refractive power. This typically involves theselection of the anterior radius and surface shape, posterior radius andsurface shape, the lens thickness, the refractive index of the lens andthe lens position in the eye. In practical terms, the lens modeling canbe performed with data based on a correction lens described in theSwedish patent application with application number SE-0000611-4, whichhereby is incorporated in this application by reference. In such a caseit is preferred to deviate as little as possible from an alreadyclinically approved model. For this reason, it may be preferred tomaintain pre-determined values of the central radii of the lens, itsthickness and refractive index, while selecting a different shape of theanterior or posterior surface, thus providing these surfaces to have anaspheric or asymmetric shape. According to an alternative of theinventive method, the spherical anterior surface of the conventionalstarting lens is modeled by selecting a suitable aspheric component.Designing aspheric surfaces of lenses is a well-known technique and canbe performed according to different principles. The construction of suchsurfaces is explained in more detail in our parallel Swedish PatentApplication 0000611-4 which is given as reference. As said before theterm aspheric in this text is not restricted to symmetric surfaces. Forexample radially asymmetric lenses can be used to correct for coma.

The inventive method can be further developed by comparing aberrationsof an optical system comprised of the mathematical models of the corneaand the capsular bag lens and the correction lens with the aberrationsof the cornea and the capsular bag lens and evaluating if a sufficientreduction in aberrations is obtained. Suitable variable parameters arefound among the above-mentioned physical parameters of the lens, whichcan be altered so to find a lens model, which deviates sufficiently frombeing a spherical lens to compensate for the aberrations.

The characterization of at least one corneal surface and the capsularbag lens as mathematical models and thereby establishing mathematicalmodels of the cornea and the capsular bag lens expressing theaberrations is preferably performed by using a wavefront sensor formeasuring the total aberration of the eye and direct corneal surfacemeasurements according to well-known topographical measurement methodswhich serve to express the surface irregularities of the cornea into aquantifiable model that can be used with the inventive method. Fromthese two measurements the aberration of the capsular bag lens couldalso be calculated and expressed in aberration terms, such as a linearcombination of polynomials which represent the aberration of thecapsular bag lens. The aberration of the capsular bag lens is determinedeither by using the wavefront aberration values of the whole eye andfrom these subtracting the wavefront aberration values of the cornea oralternatively by modeling the optical system in the following way—startwith a model of the cornea based on corneal measurements and a “startingpoint” capsular bag lens, calculate the aberrations of this system, thenmodify the shape of the capsular bag lens until the calculatedaberrations are sufficiently similar to the measured aberrations of theuncorrected eye. Corneal measurements for this purpose can be performedby the ORBSCAN® videokeratograph, as available from Orbtek, L.L.C, or bycorneal topography methods, such as but not limited to EyeSys® orHumphrey Atlas®. Preferably at least the front corneal surface ismeasured and more preferably both front and rear corneal surfaces aremeasured, characterized and expressed in aberration terms, such as alinear combination of polynomials which represent the total cornealaberrations. According to one important aspect of the present invention,characterization of corneas and capsular bag lenses is conducted on aselected population with the purpose of expressing an average ofaberrations and designing a lens from such averaged aberrations. Averageaberration terms of the population can then be calculated, for exampleas an average linear combination of polynomials and used in the lensdesign method. This aspect includes selecting different relevantpopulations, for example in age groups, to generate suitable averagecorneal surfaces and capsular bag lenses to be used to comply withindividual design methods. The patient will thereby obtain a lens thatgives the eye substantially less aberrations when compared to aconventional lens having substantially spherical surfaces.

Preferably, the mentioned measurements also include the measurement ofthe refractive power of the eye. The powers of the cornea and thecapsular bag lens as well as the axial eye length are typicallyconsidered for the selection of the lens power in the inventive designmethod.

Also preferably, the wavefront aberrations herein are expressed as alinear combination of polynomials and the optical system comprising themathematical model of the cornea and the capsular bag lens and themodeled intraocular correction lens provides for a wavefront havingobtained a substantial reduction in aberrations, as expressed by one ormore such polynomial terms. In the art of optics, several types ofpolynomial terms are available to skilled persons for describingaberrations. Suitably, the polynomials are Seidel or Zernikepolynomials. According to the present invention Zernike polynomialspreferably are employed.

The technique of employing Zernike terms to describe wavefrontaberrations originating from optical surfaces deviating from beingaberration free is a state of the art technique and can be employed forexample with a Hartmann-Shack sensor as outlined in J. Opt. Soc. Am.,1994, Vol. 11(7), pp. 1949-57. It is also well established among opticalpractitioners that the different Zernike terms signify differentaberration phenomena including defocus, astigmatism, coma and sphericalaberration as well as higher order forms of these aberrations. In anembodiment of the present method, the corneal surface and capsular baglens measurements results in that a corneal surface shape and a capsularbag lens shape can be expressed as linear combinations of Zernikepolynomials (as described in Equation (1)), wherein Z_(i) is the i-thZernike term and a₁ is the weighting coefficient for this term. Zernikepolynomials are a set of complete orthogonal polynomials defined on aunit circle. Below, Table 1 shows the first 15 Zernike terms up to thefourth order and the aberrations each term signifies. $\begin{matrix}{{z\left( {\rho,\theta} \right)} = {\sum\limits_{i = 1}^{15}{a_{i}Z_{i}}}} & (1)\end{matrix}$

In equation (1), ρ and θ represent the normalized radius and theazimuthal angle, respectively. TABLE 1 a_(i) Z_(i) (ρ, θ) a₁ 1 piston a₂2pcos θ Tilt x a₃ 2psinθ Tilt y a₄ {square root over (3)}(2ρ² − 1)defocus a₅ {square root over (6)}(ρ² sin 2θ) Astigmatism 1^(st) order(45°) a₆ {square root over (6)}(ρ² cos 2θ) Astigmatism 1^(st) order (0°)a₇ {square root over (8)}(3ρ³ − 2p)sin θ Coma y a₈ {square root over(8)}(3ρ³ − 2p)cos θ Coma x a₉ {square root over (8)}(ρ³ sin 3θ) Trifoil30° a₁₀ {square root over (8)}(ρ³ cos 3θ) Trifoil 0° a₁₁ {square rootover (5)}(6ρ⁴ − 6ρ² + 1) spherical aberration a₁₂ {square root over(10)}(4ρ⁴ − 3ρ²)cos 2θ Astigmatism 2^(nd) order (0°) a₁₃ {square rootover (10)}(4ρ⁴ − 3ρ²)sin 2θ Astigmatism 2^(nd) order (45°) a₁₄ {squareroot over (10)}(ρ⁴ cos 4θ) Tetrafoil 0° a₁₅ {square root over (10)}(ρ⁴sin 4θ) Tetrafoil 22.5°

Conventional optical correction with intraocular lenses will only complywith the fourth term of an optical system comprising the eye with animplanted lens. Glasses, contact lenses and intraocular lenses providedwith correction for astigmatism can further comply with terms five andsix and thus substantially reduce Zernike polynomials referring toastigmatism.

The inventive method further includes to calculate the aberrationsresulting from an optical system comprising said modeled intraocularcorrection lens and said mathematical models of the cornea and thecapsular bag lens and expressing it in a linear combination ofpolynomials and to determine if the intraocular correction lens hasprovided sufficient reduction in aberrations. If the reduction inaberrations is found to be insufficient, the lens will be re-modeleduntil one or several of the polynomial terms are sufficiently reduced.Remodeling the lens means that at least one of the conventional lensdesign parameters is changed. These include the anterior surface shapeand/or central radius, the posterior surface shape and/or centralradius, the thickness of the lens and its refractive index. Typically,such remodeling includes changing the curvature of a lens surface so itdeviates from being a perfect sphere. There are several tools availablein lens design that are useful to employ with the design method, such asOSLO version 5 see Program Reference, Chapter 4, Sinclair Optics 1996.

According to a preferred aspect of the first embodiment, the inventivemethod comprises expressing the shape of at least one corneal surfaceand a capsular bag lens as linear combinations of Zernike polynomialsand thereby determining the corneal and capsular bag lens wavefrontZernike coefficients, i.e. the coefficient to each of the individualZernike polynomials that is selected for consideration. The correctionlens is then modeled so that an optical system comprising said modeledcorrection lens and the mathematical models of the cornea and thecapsular bag lens provides a wavefront having a sufficient reduction ofselected Zernike coefficients. The method can optionally be refined withthe further steps of calculating the Zernike coefficients of the Zernikepolynomials representing a wavefront resulting from an optical systemcomprising the modeled intraocular correction lens and the mathematicalmodels of the cornea and the capsular bag lens and determining if thelens has provided a sufficient reduction of the cornea and the capsularbag lens wavefront Zernike coefficients; and optionally re-modeling saidlens until a sufficient reduction in said coefficients is obtained.Preferably, in this aspect the method considers Zernike polynomials upto the 4th order and aims to sufficiently reduce Zernike coefficientsreferring to spherical aberration and/or astigmatism terms. It isparticularly preferable to sufficiently reduce the 11th Zernikecoefficient of a wavefront from an optical system comprising themathematical models of the cornea and the capsular bag lens and saidmodeled intraocular correction lens, so as to obtain an eye sufficientlyfree from spherical aberration. Alternatively, the design method canalso include reducing higher order aberrations and thereby aiming toreduce Zernike coefficients of higher order aberration terms than the4^(th) order.

When designing lenses based on corneal and capsular bag lenscharacterizations from a selected population, preferably the cornealsurfaces and the capsular bag lens of each individual are expressed inZernike polynomials and the Zernike coefficients are determined. Fromthese results average Zernike coefficients are calculated and employedin the design method, aiming at a sufficient reduction of selected suchcoefficients. It is to be understood that the resulting lenses arrivingfrom a design method based on average values from a large populationhave the purpose of substantially improving visual quality for allusers. A lens having a total elimination of an aberration term based onan average value may consequently be less desirable and leave certainindividuals with an inferior vision than with a conventional lens. Forthis reason, it can be suitable to reduce the selected Zernikecoefficients only to a certain degree or to a predetermined fraction ofthe average value.

According to another approach of the inventive design method, cornealand capsular bag lens characterizations of a selected population and theresulting linear combinations of polynomials, e.g. Zernike polynomials,expressing each individual corneal and capsular bag lens aberrations canbe compared in terms of coefficient values. From this result, a suitablevalue of the coefficients is selected and employed in the inventivedesign method for a suitable lens. In a selected population havingaberrations of the same sign such a coefficient value can typically bethe lowest value within the selected population and the lens designedfrom this value would thereby provide improved visual quality for allindividuals in the group compared to a conventional lens.

According to another embodiment, the present invention is directed tothe selection of an intraocular lens of refractive power, suitable forthe desired optical correction that the patient needs, from a pluralityof lenses having the same power but different aberrations. The selectionmethod is similarly conducted to what has been described with the designmethod and involves the characterization of at least one corneal surfaceand one capsular bag lens with mathematical models by means of which theaberrations of the corneal surface and the capsular bag lens iscalculated. The optical system of the selected correction lens and themathematical models of the corneal and the capsular bag lens is thenevaluated so as to consider if sufficient reduction in aberrations isaccomplished by calculating the aberrations of a wavefront arriving fromsuch a system. If an insufficient correction is found a new lens isselected, having the same power, but different aberrations. Themathematical models employed herein are similar to those described aboveand the same characterization methods of the corneal surfaces and thecapsular bag lens can be employed.

Preferably, the aberrations determined in the selection are expressed aslinear combinations of Zernike polynomials and the Zernike coefficientsof the resulting optical system comprising the mathematical models ofthe cornea and the capsular bag lens and the selected correction lensare calculated. From the coefficient values of the system, it can bedetermined if the intraocular correction lens has sufficiently balancedthe corneal and capsular bag lens aberration terms, as described by theZernike coefficients of the optical system. If no sufficient reductionof the desired individual coefficients are found these steps can beiteratively repeated by selecting a new correction lens of the samepower but with different aberrations, until a lens capable ofsufficiently reducing the aberrations of the optical system is found.Preferably at least 15 Zernike polynomials up to the 4^(th) order aredetermined. If it is regarded as sufficient to correct for sphericalaberration, only the spherical aberration terms of the Zernikepolynomials for the optical system of cornea and capsular bag lens andintraocular correction lens are corrected. It is to be understood thatthe intraocular correction lens shall be selected so a selection ofthese terms becomes sufficiently small for the optical system comprisingcorrection lens and cornea and capsular bag lens. In accordance with thepresent invention, the 11^(th) Zernike coefficient, a₁₁, can besubstantially eliminated or sufficiently close to zero. This is aprerequisite to obtain an intraocular correction lens that sufficientlyreduces the spherical aberration of the eye. The inventive method can beemployed to correct for other types of aberrations than sphericalaberration by considering other Zernike coefficients in an identicalmanner, for example those signifying astigmatism, coma and higher orderaberrations. Also higher order aberrations can be corrected dependent onthe number of Zernike polynomials elected to be a part of the modeling,in which case a correction lens can be selected capable of correctingfor higher order aberrations than the 4^(th) order.

According to one important aspect, the selection method involvesselecting correction lenses from a kit of correction lenses havinglenses with a range of power and a plurality of lenses within each powerhaving different aberrations. In one example the correction lenseswithin each power have anterior surfaces with different asphericcomponents. If a first correction lens does not exhibit sufficientreduction in aberration, as expressed in suitable Zernike coefficients,then a new correction lens of the same power, but with a differentsurface is selected. The selection method can if necessary beiteratively repeated until the best correction lens is found or thestudied aberration terms are reduced below a significant borderlinevalue. In practical means, the Zernike terms obtained from the cornealand capsular bag lens examination will be directly obtained by theophthalmic surgeon and by means of an algorithm will be compared toknown Zernike terms of the correction lenses in the kit. From thiscomparison the most suitable correction lens in the kit can be found andimplanted.

The present invention further pertains to an intraocular correction lenshaving at least one aspheric surface capable of transferring a wavefronthaving passed through the cornea of the eye into a wavefront that whenit after passing the correction lens passes the capsular bag lens istransferred into a substantially spherical wavefront with its center atthe retina of the eye. Preferably, the wavefront is substantiallyspherical with respect to aberration terms expressed in rotationallysymmetric Zernike terms up to the fourth order.

In accordance with an especially preferred embodiment, the inventionrelates to an intraocular correction lens, which when the aberration iscalculated and expressed as a linear combination of Zernike polynomialterms, has an 11^(th) term of the fourth order with a Zernikecoefficient a₁₁ of a value that after implantation of the correctionlens sufficiently reduces the spherical aberration of a wavefrontpassing the eye. In one aspect of this embodiment, Zernike coefficienta₁₁ of the correction lens is determined so as to compensate for anaverage value resulting from a sufficient number of estimations of theZernike coefficient a₁₁ in corneas and capsular bag lenses. In anotheraspect, the Zernike coefficient a₁₁ is determined to compensate for theindividual corneal and capsular bag lens coefficient of one patient. Thelens can accordingly be tailored for an individual with high precision.

The lenses according to the present invention can be manufactured withconventional methods. In one embodiment they are made from soft,resilient material, such as silicone or hydrogels. Examples of suchmaterials are found in WO 98/17205. Manufacturing of aspheric siliconelenses or similarly foldable lenses can be performed according to U.S.Pat. No. 6,007,747. Alternatively, the lenses according to the presentinvention can be made of a more rigid material, such aspoly(methyl)methacrylate. The skilled person can readily identifyalternative materials and manufacturing methods, which will be suitableto employ to produce the inventive aberration reducing lenses.

In one preferred embodiment of the invention the intraocular correctionlens is adapted to be implanted in the posterior chamber of the eyebetween the iris and the capsular bag. The correction lens according tothis embodiment comprises preferably a centrally located optical partcapable of providing an optical correction and a peripherally locatedsupporting element capable of maintaining said optical part in saidcentral location, said optical part and said support element togetherhaving a concave posterior surface which is part of a non-sphericalsurface, the intersection between said non-spherical surface and anyplane containing the optical axis representing a flawless curve freefrom discontinuities and points of inflection. Such an intraocularcorrection lens without the inventive aberration reduction is describedin SE-0000611-4. This lens design is preferred since it is adapted tothe anatomy of the eye and avoids stress to the crystalline lens. Due toits design, contacts between the natural lens and the iris are avoidedor minimized.

The method of designing this preferred correction lens comprisessuitably the steps of:

-   -   estimating the anterior radius of the lens in the capsular bag        in its non-accommodated state;    -   selecting a posterior central radius of the correction lens        different to that of the lens in the capsular bag in its        non-accommodated state;    -   determining the total correction lens vault based on the data        arriving from steps (i) and (ii);    -   selecting a flawless curve free from points of inflection        representing the intersection of the posterior surface and a        plane containing the optical axis so as to provide an aspheric        posterior correction lens surface.

In another embodiment of the invention the correction lens is adapted tobe placed in the anterior chamber of the eye and fixated to iris. Theadvantage of this embodiment is that the correction lens is attached toiris and will not move around and has no ability to rotate thus makingit more suitable for correcting non-symmetric aberrations

The present invention also relates to a method of improving the visionof an eye. According to the invention an intraocular correction lens asdescribed above is implanted in the eye. The vision can also be furtherimproved by providing spectacles or correction lenses outside the eye orby modulating the cornea by for example laser.

The ophthalmic lenses according to the invention can suitably bedesigned and produced especially for correcting for aberrationsintroduced by corneal surgery such as LASIC (=laser in situkeratomilensis) and PRK (=photorefractive keratectomy). The cornea andthe whole eye are measured as described above on patients who haveundergone corneal surgery and the correction lenses are designed fromthese measurements. The lenses according to the invention could alsosuitably be designed for patients having corneal defects or cornealdiseases.

The described lenses according to the invention could either be designedfor each individual or they could be designed for a group of people.

The invention also refers to a method of improving the visual quality ofan eye, wherein a corneal surgery first is conducted on the eye. Thecornea is then allowed to recover before a wavefront analysis of the eyeis performed. If the aberrations of the eye have to be reduced acorrection lens adapted for this individual is designed according to thedescription above. This correction lens is then implanted in the eye.Different types of corneal surgery are possible. Two common methods areLASIK and PRK, as described in Survey of Ophthalmology, 1998, Vol. 43(2), p 147-156 by J J Rowsey et al. The presently invented method willfind particular advantage the perfect visual quality for individuals whohave undergone corneal surgery, but have outstanding visual impairments,which are considered as difficult to reach with conventional surgery.

1. An intraocular lens, comprising: an optical part configured to beimplanted in an eye of a subject; and at least one aspheric surfaceconfigured, in combination with a lens in the capsular bag of an eye, toreduce an aberration of a wavefront passing the eye.
 2. The intraocularlens of claim 1, wherein the aberration includes at least on ofastigmatism, coma, and spherical aberration.
 3. The intraocular lens ofclaim 1, wherein the at least one aspheric surface is configured toreduce a predetermined aberration coefficient below a predeterminedborderline value.
 4. The intraocular lens of claim 1, wherein anaberration of the intraocular lens is expressed as a linear combinationof Zernike polynomial terms.
 5. The intraocular lens of claim 4, whereinthe linear combination of Zernike polynomial terms includes a Zernikecoefficient a₁₁
 6. The intraocular lens of claim 5, wherein the Zernikecoefficient a₁₁ is selected to reduce a spherical aberration of awavefront passing the eye.
 7. The intraocular lens of claim 5, whereinthe Zernike coefficient a₁₁ is selected so as to compensate for anaverage value resulting from a predetermined number of estimations ofthe Zernike coefficient a₁₁ in a population of corneas and capsular baglenses.
 8. The intraocular lens of claim 5, wherein the Zernikecoefficient a₁₁ is selected so as to compensate for the individualcorneal and capsular bag lens coefficient of the subject.
 9. Theintraocular lens of claim 1, wherein the at least one aspheric surfaceis configured to reduce at least one Zernike coefficient of a selectedpopulation.
 10. The intraocular lens of claim 1, wherein the intraocularlens is characterized by one or more parameters which contribute to adetermination of a lens shape of the optical part.
 11. The intraocularlens of claim 11, wherein at least one of the one or more parameters isselected to deviate sufficiently from a spherical lens so as tocompensate for the aberration.
 12. An intraocular lens, comprising: anoptical part configured to be implanted between the cornea and thecapsular bag; and at least one aspheric surface configured to compensatefor an aberration of a wavefront passing the eye.
 13. The intraocularlens of claim 12, wherein the optical part configured to be implanted inthe anterior chamber of the eye.
 14. The intraocular lens of claim 12,wherein the optical part configured to be implanted in the posteriorchamber of the eye.
 15. An intraocular lens, comprising: a correctionlens configured to be implanted in an eye of a subject, the eyecomprising a cornea and a capsular bag lens which together arecharacterized by at least one wavefront Zernike coefficient; thecorrection lens configured, in combination with cornea and the capsularbag lens, to provide a predetermined reduction in the at least onewavefront Zernike coefficient.
 16. The intraocular lens of claim 15,wherein the at least one wavefront Zernike coefficient is at least oneof a spherical aberration term and an astigmatism term.
 17. Theintraocular lens of claim 15, wherein the at least one wavefront Zernikecoefficient is an 11th wavefront Zernike coefficient.
 18. An intraocularlens, comprising: an optical part configured to be implanted in an eyeof a subject; and at least one aspheric surface configured, togetherwith a lens in the capsular bag of the eye, to restore a wavefrontpassing the eye and deviating from sphericity into a more sphericalwavefront.